A take-up winder is a machine that winds a synthetic yarn produced by a spinning machine onto a package around the surface of a bobbin inserted into a bobbin holder. There are two types of such take-up winders, a friction-driven type that drives the rotation of a friction roller rotated in contact with a package, and a spindle-driven type that drives the rotation of a bobbin holder. In the spindle-driven type, the package forms with the yarn let out at a fixed speed from the spinning machine and, as the diameter of the package slowly becomes larger, control is required in order to gradually reduce the rotation speed of the bobbin holder and maintain a constant winding speed.
In order to control the rotation speed of the bobbin holder, a contact roller is provided which rotates in contact with the bobbin or package while exerting a fixed pressure and, at the same time, detecting the peripheral rotation speed of the package. By detecting the rotation speed of the contact roller, the peripheral speed of the package is determined, and this peripheral speed is then compared to the preset peripheral speed in order to control the speed of the bobbin holder and keep the package winding speed constant. The contact roller in this kind of spindle-driven take-up winder, which rotates in contact with the bobbin or package, has a tendency to slip, necessitating control of the rotational speed of the bobbin holder to account for these slips. However, at high winding speeds, the slips can be very large and vary greatly. Since the winder is operated at a speed that corresponds to the peripheral speed of the contact roller, when a slip occurs, the peripheral speed detected is slower than the real peripheral speed of the package. The yarn is thus wound more tightly, increasing yarn tension, and thereby causing the package to bulge or otherwise become misshapen.
Assisted driving of the contact roller has been implemented to solve this problem. To create this assisted drive, conventional winding machines may use a torque motor. A torque motor has the unique ability to decrease rotation speed when torque is large, and to increase rotation speed when torque is small. Thus, when there is a large slip of the contact roller, the contact roller's torque motor receives a relatively large amount of drive force, the load torque is reduced, and the rotation speed is increased. On the other hand, when the slip is created by the contact roller's over-driving of the package, the load torque is increased, and the rotation speed is thus decreased. Thus the torque motor is able to control the rotation speed and eliminate the slip in either event.
Conventional winders may also use an inverter-controlled variable speed motor to assist the drive of the contact roller. This variable speed motor, creating almost burdenless drive, drives the contact roller at a rotation speed calculated as a function of the rotation speed of the contact roller when it is driven only by the contact roller, the appropriate spread of the torque value from the bobbin holder to the contact roller, and the number of packages being formed.
However, both of these conventional solutions have deficiencies. Driving the contact roller by means of a torque motor does not permit precise control of the slips, and driving the contact roller by means of a variable speed motor which rotates the roller at speeds according to a predetermined fixed function means that, whenever the specifications of the machine are changed, the fixed function of the variable speed motor mist also be changed accordingly.